[foreign-jextract] RFR: 8268319: VersionCheck test fails for jextract on Windows

[Jorn Vernee]

The test tools/launcher/VersionCheck fails for jextract on Windows, because the filtering logic to filter out warnings in the output checks that the executable file name is "jextract", while on Windows it's "jextract.exe". So, the warnings are never filtered

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Commit messages:
 - Fix VersionCheck test on Windows

Changes: https://git.openjdk.java.net/panama-foreign/pull/552/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=552&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268319
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/552.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/552/head:pull/552

PR: https://git.openjdk.java.net/panama-foreign/pull/552